Lighting systems, such as lighting systems for aircraft, are known. Lighting systems are generally required on aircraft for use as landing lights, taxi lights, search lights and so on. These lighting systems are used, for example, to better illuminate the runway during take-off and landing under low-light conditions.
A lighting system incorporates a light source. For certain applications, the light emitted from a light source must be directed in a particular manner, for example to control the spread and orientation of the emitted light. In order to properly direct the light emitted from the light source, a lens is used.
The spatial and optical parameters of the lens used to control the output light are of the upmost importance. As such, the lens may be formed from a material that has been selected to have advantageous optical and formability properties. One example of a material that may be used to form a lens is liquid silicone rubber (LSR).
In particular, liquid silicone rubber (LSR) has good optical properties and good formability properties, thereby allowing for the formation of complex lens shapes. Liquid silicone rubber also weighs less than some other materials that may be used to form lenses, such as glass, and may therefore be preferred in certain applications for this reason. However, despite the advantageous optical and formability properties associated with liquid silicone rubber, liquid silicone rubber also has some disadvantageous properties. For example, some forms of liquid silicone rubber may have a relatively lower Young's modulus (less than 0.05 GPa) and lower hardness rating (around 5 to 90 on the Shore A hardness scale) compared to other optical materials such as Poly(methyl methacrylate) (PMMA), which may have a Young's modulus of around 1.8 to 3.1 GPa and a hardness rating of around 90 to 100 on the Shore D hardness scale or Polycarbonate, which may have a Young's modulus of around 13.5 to 21.4 GPa and a hardness of around 80 on the Shore D hardness scale.
These relatively poorer structural properties of liquid silicone rubber means that it can be difficult, during assembly of a lighting system, to accurately position the liquid silicone rubber lens in a desired position relative to the light source. Furthermore, if the lighting system including the liquid silicone rubber lens is incorporated into a vehicle such as an aircraft, vibration caused by the vehicle's motion may displace or otherwise distort the liquid silicone rubber lens relative to the light source, thereby reducing the optical performance of the lighting system.
It would therefore be desirable to improve the structural properties of lenses formed from liquid silicone rubber.